The oral mucosa is directly challenged with Human Immunodeficiency Virus (HIV) by exposure of infants to HIV-carrying vaginal fluids at birth and to breast milk postnatally, and with passive oral sex among men. Exposures commonly include both X4 and R5 HIV, yet R5 viruses account for most primary systemic infections. When exposed to HIV and Porphyromas gingivalis cysteine proteases, we hypothesize that oral keratinocytes up-regulate expression of innate immune molecules, including alpha- and beta-defensins and other associated genes, to enhance HIV R5 transcytosis and intracellular resistance to HIV infection. To test this hypothesis, we will: 1. show that expression of CXCR4 and CCR5 by oral keratinocytes contribute to coreceptor-specific transcytosis of X4 and R5 HIV isolates; 2. determine if exposure to HIV regulates expression of the innate immune molecules calprotectin and alpha- and beta-defensins directly or in association with PAR signaling mediated by specific P. gingivalis protease mutants; 3. identify and profile oral keratinocyte innate immune-associated gene expression patterns, including known plausible HIV co-receptors and other innate immune molecules, which are regulated by HIV in the presence and absence of P. gingivalis proteases; and 4 show how innate immune molecules modulate transcytosis, translocation by paracellular routes, and anti-HIV resistance in oral keratinocytes in vitro. This project will show that oral keratinocytes express innate immune molecules to resist intracellular infection by X4 and R5 HIV. In the presence of cysteine proteases, innate immune molecules and genes required for transcytosis of R5 HIV expression will be up-regulated, increasing intracellular anit-HIV resistance and facilitating transfer R5 HIV-1 to initiate systemic infection. Innate immune factor-related genes may prove to be novel targets to prevent mucosal HIV.